Fuel gauging system for weightless tankages



, R W. 4 6 l O L 6 6 R 2 t .H 4 m S 0 e CD N N 6 e M A m n e E E T 8 T C W. L 1 L C u, m QfA m m F N m 2 Z w m 1 s w M J S A. B Sm 4 www mml 3 6 6 I.. V FN; m GY 4 5 5 N u lil f I 6 M w NR om/m 2 l .lr" 4 c 5 m H* O M El E 1 MC rr- T Q S 2 J M H A 1; G N R m m m .a. R S L U M M E BA u MH r F O C C n June 25, 1968 Flled Aprll 20, 1964 June 25, 1968 Filed April 2o, 1964 souNo l souRcE J. E. CLEMENS FUEL GAUGING SYSTEM FOR WEIGHTLESS TANKAGES 2 Sheets-Sheet '.f;

111/ l l ll 111/ i ffm INVENTOR.

JQHN E. CLEMENS AGENT United States Patent O 3,389,602 FUEL GAUGING SYSTEM FOR WEIGHTLESS TANKAGES John E. Clemens, Xenia, Ohio, assignor to Industrial Nucleonics Corporation, a corporation of Ohio Filed Apr. 20, 1964, Ser. No. 361,060 18 Claims. (Cl. 73-290) ABSTRACT F THE DISCLOSURE A fuel gauge for a fuel tank intended for use in a zero gravity environment. The tank is of the type having one or a plurality of baflles near the outlet of the tank so that when the tank is nearly empty the remnant fuel because of the effect of capillary attraction collects within the conlines of the bailles. A liquid level probe is located within each baille so that an accurate summation of the remaining fuel can be made. The probes can be of a known type such as capacitance, sonic or radiation attenuation or of a special ionization gauge disclosed herein. When the latter type is used the structure of the guage itself can form the baille structure of the tank.

This invention relates to liquid fuel gauges and more particularly to apparatus for measuring the amount of fuel in the storage tank of a space vehicle during periods of weightlessness.

Modern-day space vehicles and intercontinental ballistic missiles are powered in the main by either solid or liquid fuels. These fuels are Iburned in a combustion chamber and expelled through a nozzle to propel the vehicle along a prescribed trajectory or orbit. The solid propellants do not pose the same handling problems that liquid fuels do. For example, liquid propellants must be stored in a tank and pumped from there to the rocket engine, while solid propellants can be stored in the combustion chamber and burned therein. Once the entire launching package has left the pad and staging of the several engines has occurred, the space vehicle will -coast in free flight at a velocity which will either cause it to orbit the earth or give it a trajectory terminating in a predetermined impact area. In any event, during free-flight, the vehicle experiences weightlessness that has caused many problems, especially in manned space missions such as the recent Project Mercury series sponsored by the National Aeronautics and Space Administration.

One of these problems is that it has been difficult to control the liquid fuel stored in the vehicle since it tends to break up and randomly orient itself around the tank. It has been impossible to know how much fuel remains in the tank because of its random orientation therein. Moreover, the fuel may be located away from the pumping outlet at a time when thrust is needed for a roll, pitch or yaw correction. To cure this last mentioned problem, it has been proposed to confine the liquid by a variation of the capillary tube technique described in NASA Technical Notes D-l577 and D-1582, written by Donald A. Petrash et al. and published in January 1963. Briefly, various geometrical bafllles are mounted over the pumping outlet to control the liquid-vapor interface in the tank. By constructing the baffles of a predetermined size and shape relative to the tank, it is possible to make the liquid continuously till the baille instead of flying around the tank. Essentially, the liquid tends to assume a configuration that makes the total surface energy a minimum. The bailles are usualy of different size so that the smallest baille fills first and empties last.

Since the fuel is already confined in these baffles to make it immediately available for pumping to the engines, it is proposed to lmeasure the iill level of each of Cil rice

these bailles in order to determine the amount of fuelremaining. It is appreciated that unless the combined capacities of the bailles is suillcient, there lwill be some fuel located outside the baiiles that cannot be measured. It is therefore primarily when enough fuel has been used that all the remaining fuel will be located in the bailles that the present invention has particular utility. It is usually the case that greater accuracy of measurement is required at low fuel levels.

A number of different baille level detectors are described. One type provides a unique ionization chamber construction that is integral with the baille itself.

Accordingly, it is a primary object of the present invention to provide a fuel gauging system for a space vehicle operating in a zero-G environment.

It is another object of the present invention to provide a liquid level gauge that is more accurate than similar devices used heretofore.

It is yet another object of the present invention to provide an improved liquid fuel gauging system that is simple to construct.

It is still another object of the present invention to provide an improved liquid fuel gauging system that can be constructed of lightweight materials thereby reducing the payload requirements of launching equipment.

Other objects and advantages of the present invention will become more apparent upon reference to the following description when taken in conjunction with the drawings, in which:

FIG. l is a sketch of a space vehicle subject to periods of weightlessness;

FIG. 2 is a block diagram of a typical propulsion apparatus for the vehicle shown in FIG. 1 illustrating schematically the fuel gauging technique of the present invention;

FIG. 3 is a sectional view of a liquid fuel baille useful in explaining the operation of the present invention;

FIG. 4 is an elevation of a concentric cylinder fuel baffling and measuring system constructed in accordance with the present invention;

FIG. 5 is a top View of a multi-cylinder fuel baille;

FIG. 6 is a top View of a variable-size sector fuel baille;

FIG. 7 is a diagrammatic elevation view, partly in section, showing an alternative fuel measuring system;

FIG. 8 is a diagrammatic elevation view, partly in section, showing another fuel measuring system;

FIG. 9 is an elevation view, partly in section, of a radiation fuel height gauge of novel construction; and,

FIG. l0 is an elevation View of a fuel gauging system combining the plural baflle arrangement of FIG. 4 and the fill height gauge shown in FIG. 9.

With reference now to the drawings and particularly to FIG l, there is shown a typical space vehicle launching operation. A rocket 10 is fired from a launch pad L for the purpose of either placing a payload such as a capsule 12 in orbit or striking an earth-based target T with a nuclear warhead 14. A control block-house 16 relays and receives data from the rocket or satellite via an r.f. link 18 concerning, for example, information on the trajectory 20. The rocket 10 spends most of its time in freeflight when used as a ballistic missile. The capsule 12 is weightless except during launch and re-entry.

These extended periods of weightlessness or zero-G make it diilicult to know how much fuel remains available either to correct the trajectory 20 of the warhead or to maintain the orientation and attitude of the capsule 12. Referring to FIG. 2, a conventional propulsion system includes a fuel tank 22 and a combustion chamber 24. The combustion chamber 24 may be simply a hydrogen peroxide jet for correcting a capsule roll, for example. A pump 26 serves to transport liquid fuel from the tank 22 through a line 28. The fuel in the tank 22 may be or hypergolic fuels commonly used. Under zero-G conditions, the liquid fuel splashes around the tank 22 and makes it difiicult to determine the quantity of fuel left to complete a mission. To keep lthe fuel confined to a known region 22a of the tank for measurement, the present invention provides a-capillary baffle 30 described in detail hereinafter. If thereis any fuel in the tank, it will be in the baffle. Therefore I mount a probe I3,2 inside the bafiie to sense the amount of fuel therein. Measuring circuitry 34 is coupled to the probe 32 and develops a fuel quantity signal on line 36 that can be either read out on a pilots display device 38 or telemetered back to the block-house 16 for facilitating optimum trajectory-computations.

The bales 30' will hold thefuel under zero-G and up to small g-loadings before it loses control. During these periods, the sensor 32 and associated circuitry will pro vide an accurate indication of the amount of fuel in the baflie. Moreover, the fuely outlet 28 communicates with the baffle 30 so that if there is any fuel in the tank, it will be immediately available for consumption. Obviously, the measuring system can detect no more fuel than can be held inthe bafiie 30, but it is usually only necessary to be aware of a low fuel condition.

Before the construction of the fuel bafiie 30 is taken up, consider the forces existing in a typical capillary system such as one cylinder 31 mounted within another as shown in FIG. 3. The direction of liquid motion in a capillary system such as that shown in FIG. 3 may be derived from a consideration of either capillary forces or surface energy. Because each method provides insight into behavior of the system, each will be derived hereinafter. v

A sketch of a capillary system of the type under consideration', presents a general situation of a liquid with a contact angle and shows the forces, pressures, and system radii. lf capital letters are used to denote quantities applicable to the annulus and small letters those applicable to the inside of the tube, the following equations may be written for the vertical forces at the solid-liquidvapor interfaces:

where a'lv is the energy per unit area coefficient associated with the liquid-vapor interface and r is the inside radius of the tube, and

PFP: MR2-f2) R-r The pressure difference tending to drive liquid up or down the tube (Pa is common to both surfaces) is found as follows:

More simply,

Itis interesting to note that Equation l is independent of gravity. Thus the direction of liquid motion is the same in Zero gravity as in a gravity field; only the height of the liquid rise is affected by the gravity level.

Although Equation l adequately describes the direction of fiuid motion, a betterk insight into'the energy relation is obtained byv deriving the relation for fluid movement in terms of the surface energies. Consider a change in liquid height in the tube All. The change in energy on the inside tube surface As will equal the gain in energy due to covering the area Aa with liquid minus the loss in energy due to the loss in vapor wetted area:

where als and evs are the energy per unit area coefficients associated respectively with the solid-liquid and vapor- :solid interfaces. The values of the quantities U15 and cvs are unknown; however, they are related to the surface energy of the liquid and the contact angle by the Young- Dupre equation:

v rvs-415:6, Cos 0 (3) Substituting this expression in Equation 2 gives v As=Aa ab, cos 0 (4) By a similar process for the annulus (considering an upward rise) the following is obtained:

AS=AA al, cos 0 The annular height change AH can be obtained in terms of the tube height change as follows:

T2 hR2 T2 Substituting this expression in Equation 7 yields T2 R-r (8) The total energy change in the system is obtained by adding the energy changes As and AS as follows:

AS=21r Aha,v cos 0 l l A A -2 2 s-l- S arr Ahalv eos 9L, R r:| (9) The premise that the liquid-vapor system will seek a configuration of minimum total energy requires that the sum of the energy changes AS-i-AS be negative. This condition is obtained in Equation 9 if the multiple of Alz, cos 0, and

is positive. The term Ah was taken as positive in the upward direction; thus for 0 0 90 the liquid will rise in the tube if r R/2, remain stationary if r--R/ 2, and fall if r R/2. For 0 l80 the opposite situation is obtained. It is observed that the system breaks down for 0:90 since the forces involved go to zero.

In accordance with my invention, I measure the fill height of the fuel in an inner cylinder, bafiie 31. During zero-G conditions, it will be` completely filled if the radii .are properly chosen. At high ullages all of the fuel will be in the bafiie which will be somewhat less than cornpletely full. The present invention provides little utility when some of the fuel lies outside of the baie. But it is usually only necessary to be notified only of a low fuel condition in which case the baille with proper design will contain all of the available fuel.

The capacity of the baille can be increased by adding one or more cylindrical bailles in the manner illustrated in FIG. 4. Here an inner baille 44 is surrounded by an intermediate baille 46 and an outer baille 48. For convenience in pumping fuel under zero-G conditions, the bailles may be mounted over a fuel manifold comprising a plurality of outlet pipes 50, 51, and S2 communicating with the interior of the bailles and terminating in a common conduit 54 via a pair of one-way valves S3. Alternatively, openings in the bottom of the bailles would allow fuel to ilow from one baille to an inner one thereby eliminating the need for valving and manifolding devices. If the fuel is of the wetting variety, approaches 0. If R1, R2 and R3 are the radii of the iner baille 44, the intermediate baille 46 and the outer baille 48, respectively, and constructed so that R1 2R2 4R3, the innermost baille 44 is the first to fill up and the last to empty. Therefore, the manifold drains the bailles from the outside in. It should be noted that the capillary fuel management technique described herein is most useful with small tanks as the holding force of the baille walls is a function of their area while the mass of the fuel increases according to the volume thereof. The fuel will remain in the baille under slight g-loadings that occur during a yaw or a pitch correction, but a sustained thrust of the main engines will very likely dislodge the fuel from the baille and the gauge reading is not accurate.

One type of fuel level sensor may use elongated capacitance probes 56, 58 and 60 (FIG. 4) suspended down the length of each baille. Each probe may include a pair of electrodes with the fuel serving as a dielectric. It may be observed that under zero-g,7 conditions in space the contact angle 0 is preserved the same as it existed before launch; however, the surface assumes a constant curvature. Each probe must therefore be located away from the baille wall to measure the liquid at a point where the surface would be if it were level. The curvature could, of course, be compensated for in the calibration of the instrument. The effective capacitance of probe 58 changes as the fuel level drops in the intermediate baille 46. Each probe has a capacitance proportional to the volume it measures. The total capacitance of all three probes wil then be proportional to the total amount of fuel in the bailles. A bridge circuit 62 driven by an oscillator 64 can be used to determine the combined probe capacitance. The total capacitance value can be indicated on a meter 66. A more detailed description of a liquid depth gauge of this type can be found in U.S. Patent 2,941,403 issued .Tune 2l, f

1960 to I. Steenfeld et al. Y

My invention can be used with other than concentric cylindrical bailles. For example, FIG. shows a fuel tank 67 containing a plurality of separate tubes 67a-67d and FIG. 6 shows a cylindrical baille 68 having a plurality of chambers of decreasing size 6Sa-68e to provide the aforesaid fuel confinement under zero-G conditions.

My invention is neither restricted to a particular baille configuration nor to the capacitance level gauge described above. It is obvious that there are numerous geometrical constructions that can provide the fuel confinement. The number of different fuel gauges that can be used is equally abundant. Having already set forth several baille constructions, I will now describe several useful fuel level measurement devices. For simplicity, these devices are illustrated measuring the fuel level in a single cylindrical baille such as the inner baille 44 of FIG. 4. Their application to the plural baille arrangement will be apparent to those skilled in the art.

Referring iirst to FIG. 7, a source of sound waves 70 is connected to a junction 72 at the upper end of a long strip 74 extending the length of the baille 44. A plurality of holes .76 are provided down the strip to reflect sound waves propagating down from the junction 72. A transducer element 78 receives the reflected waves and gencrates a signal pulse over line 80 connected to the input of an oscilloscope 82. Those holes that are submerged in the fuel will not reflect energy back up to the transducer. The reflected pulses can be read out, as they are spaced in time due to their different path lengths. The latest pulse received is indicative of the position of the interface. This technique is described in detail in U.S. Patent 2,787,160 issued Apr. 7, 1957, to H. Van Valkenburg.

FIG. 8 illustrates a radiation fill height gauge which includes a source of a radiation 84 and an elongated detector 86 such as a G-M tube. The detector is mounted on the outside of the baille 44 opposite the source 84. Radiation striking the detector causes a current to ilow which can be measured at 88 and indicated by a meter 90. As the fuel level drops, more radiation hits the detector and a higher current is indicated. A tapered block of shielding material 91 may be mounted between the source 84 and the baille wall to linearize the relationship between fill height and detector response. This is described further in U.S. Patent 3,098,154 issued July 16, 1963, to lack G. Crump and assigned to the same assignee as the present invention. To measure the fill height of two outer bailles 46 and 48 of FIG. 4, it is necessary to pass the radiation beam across a chord of these bailles so as not to ymeasure the contents of the inner baffle 44.

FIG. 9 illustrates a preferred radiation illl level gauge that is described and claimed in my copending application Scr. No. 361,032 filed Apr. 20, 1964 and assigned to the sam-e assignee as the present invention. The gauge assentially employs a multiple ionization chamber construction. As usually constructed, an ionization chamber includes a pair of separated electrodes having an electric potential impressed thereon. The space between the electrodes is occupied by a gas such as argon which ionizes when subjected to radiation thereby enabling current ilow between the electrodes. By monitoring the amount of current ilowing it is possible to ascertain the strength of the radiation field at the detector. A material having a property to be measured is placed in the gap between the radiation source and the chamber to modulate the source field in accordance with the variations in the property. However, in the presentv invention, the source of radiation comprises one electrode of the chamber and the fluid to be measured occupies the space between the chamber electrodes.

In the construction of gauge 92, a hollow cylindrical housing of electrically insulative material substantially encircles a center electrode 94. A plurality of electrically conductive rings 96 are embedded in the housing and a battery 97 is connected between the center electrode and each of the rings 96 to provide a polarizing potential. A radioactive substance such as strontium is coated onto the center electrode 94 to ionize the vapor above the fuel. The radiation field 98 causes a substantial electrical current to ilow in those rings not immersed in the fuel. A microammeter 100 in series wih the battery 97 and a current limiting resistor 102 can be used to indicate the liquid level in the gauge 92. The magnitude of current flow is inversely proportional to the lill level which can be measured to an accuracy within the granularity of the ring spacing. It can be seen that each ring together with the center electrode 94 constitutes an ionization chamber.

In zero-G applications with which we are here concerned, the gauge itself maybe used as a fuel baille; however, since the diameter of the housing must be kept small to obtain a sensitive instrument, it may be advisable to use the gauge 92 as a fuel probe that can be mounted directly in the fuel bailles. FIG. l0 shows three such probes 104, 106 and 108 inserted in cylindrical bailles 110, 112 and 114. The probes each generate a current proportional to the volume of fuel it measures. The outputs of all the probes can be connected to a current summing amplifier 116. An indicator 118 reads the total probe current which is directly proportional to the baille ullage. It may be necessary to provide a vertically extending slot 105 in each probe to keep the probe itself from becoming an effective baille. Alternatively, a semicylindrical probe construction could be utilized.

Many other modifications may be made to the preferred embodiments of the present invention without departing from the true spirit and scope thereof or relinquishing any of the advantages attendant thereto.

I claim:

1. A gauge for measuring fuel in a partially illled tank, comprising:

a tank for storing said fuel,

capillary baille means mounted inside said tank for confining said fuel during zero-G conditions,

probe means adjacent to said baille means for measuring the amount of said fuel in said baille means, and

means coupled to said probe means for providing a signal indicative of the amount of fuel in said baille means. 2. A fuel gauge as set forth in claim 1 in which said probe means comprises a capacitance gauge.

3. A fuel gauge as set forth in claim 1 in which said probe means comprises:

a source for generating sound energy, a strip positioned longitudinally in said baille and having a plurality of holes for reflecting sound energy,

means coupling said source to said strip for propagating said sound energy downwardly along said longitudinally positioned strip toward said confined fuel, and

means receiving said strip-reflected sound energy and responsive to the arrival time relative to the time of generation thereof for indicating the level of said fuel in said tank. 4. A fuel gauge for a space vehicle having a tank for storing fuel comprising:

capillary baille means mounted inside said tank for confining said fuel during zero-G conditions, and

probe means adjacent to said capillary baille means for providing a signal proportional to the amount of fuel confined in said baille means.

5. A fuel gauge for a space vehicle, comprising:

a tank for storing said fuel,

capillary baille means mounted inside said tank for confining said fuel during zero-G conditions,

probe means adjacent to said capillary baille means for measuring the height of said fuel in said baille means, said probe measuring means including,

a radioactive source providing a beam of penetrating radiation directed into said baille and a detector positioned to receive radiation passing through said baille and said confined fuel and lmounted longitudinally along the upright dimensions of said tank,

means responsive to the radiation received by said detector for developing a signal indicative of the level of said fuel in said baille, and

means receiving said detector signal for indicating the total amount of fuel in said baille.

6. A fuel gauge for a space vehicle having a tank for storing fuel comprising:

a tank for storing said fuel,

baille means inside said tank for confining said fuel during zero-G conditions,

radiation probe means including,

a cylindrical housing mounted inside said baille means, having openings permitting said fuel to partially submerge said housing and extending axially of said baffle from the bottom thereof,

a plurality of outer electrodes mounted down the inside of said cylindrical housing in vertical alignment, and

an inner electrode emitting radiation toward said outer electrodes,

circuit means for impressing an electric potential across said inner electrode and said outer electrodes,

of said housing. v

8. A fuel gauge as set forth in claim 6 in which said center electrode comprises:

a wire coated with a beta-emitting radioisotope.

9. Apparatus for measuring the amount of fuel in a tank during zero-G conditions comprising:

a plurality of capillary baille means mounted inside said tank to confine said fuel during said zero-G conditions,

a plurality of probes each mounted adjacent to a separate one of said capillary baffle means for producing a signal indicative of the amount of fuel in said baille, and

means responsive to said signals for indicating the total amount of fuel in said plurality of bailles.

10. Apparatus as in claim 9 wherein each of said baille means has a different cross-sectional area, whereby said bailles are adapted to contain different amounts of fuel when filled.

11. Apparatus as in claim 9 in which said plurality of capillary baille means comprise: i

a plurality of concentric cylinders of different radii.

12. Apparatus as set forth in claim 9 in which said capillary baffle means comprises:

a plurality of concentrically mounted cylindrical bailles, each of said inner bailles having a radius less than one-half the radius of an outer bailles immediately surrounding said inner baille.

13. Apparatus for measuring the amount of fuel in a tank during zero-G conditions, comprising:

a plurality of capillary bailles mounted inside said tank, each of said bailles having a different cross-sectional area to confine said fuel during said zero-G conditions,

a plurality of probes each mounted adjacent to a separate one of said capillary bailles for producing a signal indicative of the amount of fuel in said baille, and

means for combining said signals to provide an indication of the total amount of fuel in said bailles.

14. Apparatus for measuring the amount of fuel in a partially filled tank of a space vehicle during zero-G conditions, comprising:

a plurality of cylindrical capillary bailles mounted inside said tank, each of said bailles having a different cross-sectional area to confine all of said fuel during said zero-G condition,

a plurality of radiation pro-be means each positioned in one of said bailles to provide signals proportional to the amount of fuel in each of said cylindrical bailles,

amplifier means for summing said signals to provide an output signal, and

means responsive to said output signal to provide an indication of the total amount offuel in said tank.

15. Apparatus as in claim 14 in whicheach of said radiation probe means comprises: p

an inner electrode emitting radiation and extending down the length of said baille, and

a plurality of outer electrodes spaced from said inner electrode and positioned in vertical alignment down the length of said baille, each of said outer electrodes not submerged in said fuel providing a flow of electrical current.

16. Apparatus as set forth in claim MWherein said 9 10 baflies are mounted over the fuel outlet of said tank to means responsive to said electrical current flows for provide a supply of fuel under zero-G conditions. indicating the total amount of fuel in said bafile.

17. Apparatus as in claim 14 wherein said baffles comprise: a plurality of concentrically ,mounted cylinders, References Cited each of said inner cylinders having a radius less than one- 5 half the radius of ari outer cylinder immediately sur- UNITED STATES PATENTS foundmg Said Inner Cy11f1df- 2,787,160 4/1957 vaikenburg 73-290 18. Apparatus for measuring the amount of fuel in a 3237'451 3 /1966 Haef 73 290 partially lled tank during zero-G conditions, comprising: 3,279,253 10/1966 Blackmon et aL 73 304 a baie including 10 1.) il,

a generally cylindrical housing mounted within said OTHER REFERENCES y H tank for confining said fuel during said zero-G condi- Petrach et al N A s A Technical note D 1577 Jam U/ u tions .f

uary 1963. Pages 2, 3, 4, 11, 12, 13 and 14 relied upon. I; a lsilaftsafdflmdes mounted dow the m 15 Copyin sciemie Library, TL 521A35t. fr/,t

aneilreigergceesctrode emitting radiation toward said outer D AVID SCHONBERG Primary Examiner.

circuit means for impressing an electrical potential be- LOUIS R PRINCE, Exame,.

tween said inner electrode and said outer electrodes to cause a ow of electrical current in those outer 20 S. C. SWISHER, Assistant Examiner. electrodes not submerged in said fuel, and 

